Japanese Patent Application Publication No. 2015-104163 (Patent Literature 1) and International Publication No. WO 2015/064572 (Patent Literature 2) each describe a semiconductor device in which a stack of a cooler and a semiconductor module is pressurized in a stacking direction thereof by a spring. The semiconductor device of Patent Literature 1 employs a plate spring curved in an arc shape. The plate spring is interposed between a pair of support posts provided in a casing and the stack. Both ends of the plate spring respectively contact the pair of support posts, and a center of the plate spring contacts an end surface of the stack in the stacking direction. The plate spring thereby applies pressure to a center of the end surface of the stack, and thus the pressure distributes unevenly on the end surface.
The semiconductor device of Patent Literature 2 employs two types of plate springs to pressurize the stack. Each of the plate springs is curved in an arc shape, and is interposed between an end surface of the stack and an inner wall of a casing. A first plate spring has its center in a longitudinal direction contact the stack, and has its both ends contact the inner wall of the casing. A second plate spring has its center in the londigudinal direction contact the inner wall of the casing, and has its both ends contact the stack. The first plate spring applies pressure to a center of the end face of the stack, and the second plate spring applies pressure to both ends of the end surface of the stack. A mere use of the first plate spring would make the pressure high at the center of the end surface and low at the both ends. By adding the second plate spring, pressure concentration at the center of the end surface of the stack can be reduced.